1. Field of the Invention
The present invention relates to a constitution of cover glass, more particularly to a cover glass having the properties of high strength and resistance in abrasion and scratch, without inclusion of environmentally unfriendly ingredients as As2O3 or Sb2O3.
2. Brief Description of the Prior Art
Nowadays, the cover glass used in touch panel and LCD of mobile facilities such as mobile phone, tablet or notebook PC is aluminosilicate glass, which is further strengthened by ion exchange process. This glass constitution contains only a trace amount of alkali metal oxides and the glass can be manufactured by forming method of float process or downdraw process.
A glass compositions disclosed in the Taiwanese Patent Gazette No. I252844 contains As2O3 and Sb2O3, harmful to human body and environment. If As2O3 and Sb2O3 are substituted by different compositions, the original optical and physical properties of glass will be changed. Therefore, extensive research and development should be conducted on the ingredients and their weight percents of glass compositions so as to solve the problem.
When the temperature of melting glass is reduced during forming process, the glass tends to generate crystallization phenomena which may cause devitrification (i.e., lose transparency due to crystal precipitation of glass). The maximum temperature at which a glass starts the devitrification or the initiate crystallization is referred to as Liquidus Temperature, LT. In order to avoid devitrification which generates negative effect on the appearance of glass, the glass liquidus temperature requires to be as low as possible. Thus, when the operating temperature is higher than the glass liquidus temperature, devitrification or crystallization will not occurred even after a long time heat treatment, otherwise prone to devitrification or crystallization which leads to impurities generation on the surface or in the interior of the glass. This will result in change of stress distribution inside glass, reduction of glass hardness and strength, deterioration of yield rate. One such example is the glass disclosed in Taiwanese Patent Gazette No. I305768, in which the liquidus temperature is higher than 1000° C. Thus, the glass has a worse stability.
Further, the melting temperature of raw material in melting process is required to be as low as possible so as to reduce energy consumption and to increase lifetime of blast furnace. In a glass disclosed in Taiwanese Patent Gazette No. 200637800, complete melting of raw materials couldn't be realized until the temperature reaches 1600° C. or above. Therefore, energy consumption is high, and manufacturing cost down is almost impossible.
In view of the above disadvantages of conventional glass, the present invention proposes a novel constitution of cover glass in which environmentally unfriendly compositions such as As2O3 and Sb2O3 can be substituted by adding or changing proportion of compositions, and then a cover glass having devitrification resistance can be produced so as to solve the problem of inconsistency with environmental standard.